Agreement between equations estimating glomerular filtration rate in elderly nursing home residents and in hospitalised patients: implications for drug dosing

Design: observational study. Setting: comparison between NH residents and H patients. Subjects: we used data from 177 NH residents, and 439 H patients. Methods: the agreement between estimating equations and the odds of a discrepancy > 25% between formulas in relation to setting (NH versus H) were investigated. Results: the agreement between MDRD and CKD-EPI formulas was good either in NH (k = 0.82) or H (k = 0.87) patients, while corresponding figures for CG indicate only a fair agreement with CKD-EPI (k = 0.50 for both populations). Setting (NH versus H) was associated with discordance between MDRD and CKD-EPI (OR = 3.97; 95% CI = 1.75-9.01), but not between CG and EPI (OR = 1.25; 95% CI = 0.87-1.81). Conclusions: in NH residents, MDRD and CKD-EPI formulas yield highly concordant GFR values, but CG behaves differently in up to one-third of patients. Such findings have important implications in dosing drugs cleared by the kidney. Setting should be taken into consideration in studies for validation of GFR equations.